1. Field of the Invention
The invention relates to piezoelectric devices and, more specifically, piezoelectric motors, being electric motors using piezo crystals for providing rotational momentum to a rotor part of the motor relative a stator part of the motor.
2. Description of the Prior Art
A piezoelectric motor is known from U.S. Pat. No. 4,453,103, granted Jun. 5, 1984, comprising a stator and a rotor, which are in mechanical contact with one another along at least one cylindrical surface of friction interaction. Elastically curved, longitudinally elongated plates/pushers, which are set against the friction surface at one end, and are positioned at an angle to the same surface, while being anchored at the other end, either directly or via a metal membrane, to the cylindrical surface of the ring piezoelectric element with electrodes for exciting longitudinal oscillations of the perpendicular surfaces of friction interaction.
A piezoelectric motor (U.S. Pat. No. 4,959,580, granted Sep. 25, 1990) is also known, possessing the same attributes, except that the pushers are at one end anchored on the flat surface of the ring piezoelectric element.
The maximum power which can be supplied to the piezoelectric element of the above motors is determined by the maximum breaking strength of the piezoelectric element or the strength of the bond between the electrodes of the piezoelectric element coating and the ceramics, when the pushers are anchored on the piezoelectric element""s surface. A small diameter of the piezoelectric element will not allow a large number of pushers to be anchored in order to increase the motor""s torque moment. Solving the above problems requires increasing the diameter of the piezoelectric element and, consequently, the piezoelectric element""s volume, which significantly increases the motor""s size and cost. The presence of recesses in the piezoelectric element and the thermal shocks that the piezoelectric ceramics is subjected to when the pushers"" connections are being soldered on it, notably reduces the motor""s reliability, especially in the modes of operation approaching the limit of tolerance. Moreover, such is the technology of anchoring pushers that it requires sizable expenditures when each new type of motor is introduced to the manufacturing process.
The main purpose of the invention is to provide a piezoelectric motor designed so that it would be possible to avoid direct connection between the pusher and the piezoelectric element.
It has been shown that if two flat ring plates are pressed against the surface plate of the piezoelectric element by means of a clamp, the plates together with the piezoelectric element will form a new oscillation system. The quality factor of the first resonance oscillation mode is not lower (and at times higher) than that of the first mode of the ring piezoelectric element, with the resonance characteristics remaining monofrequency, i.e. acting as a single whole in regard to the oscillations of the piezoelectric element with the plates, but, since the piezoelectric element is drafted, its rupture strength increases. Besides, the motor""s reliability and the maximum value of its pulse power also increase. The number of pushers can now be vastly augmented, as well as the motor""s starting torque. All this is achieved with the minimum amount of piezoelectric ceramics and at but insignificant costs of technological rigging.
In the invention, a piezoelectric motor comprises a stator and a rotor, the stator and the rotor being in mechanical contact with one another along at least one cylindrical friction surface by means of curved, elastic and longitudinally elongated pusher plates. The pusher plates are held against the friction surface at a first end of the pusher plates, and arranged at an angle to the friction surface. Further, a piezoelectric element is connected to the rotor, according to a first embodiment of the invention. The piezoelectric element has electrodes placed on opposing surfaces of the piezoelectric element, and is connectable to an alternating current source via the electrodes, for providing longitudinal oscillations in the piezoelectric element. A first ring plate and a second ring plate are arranged on opposite sides of the piezoelectric element, so that at least a portion of surfaces of the piezoelectric element are pressed against surfaces of the first ring plate and the second ring plate, respectively, by a clamping device. In this way, longitudinal oscillations are transferred into the first ring plate and the second ring plate from the piezoelectric element. At least one of the first ring plate and the second ring plate are in mechanical contact with a second end of the pusher plates.
Three alternative methods of attaching the pusher plates to the ring plates are preferred for the first embodiment of the invention:
1) The pusher plates are anchored on the first ring plate at the second end of the pusher plates.
2) The pusher plates are anchored on the second ring plate at the second end of the pusher plates.
3) A first set of the pusher plates are anchored on the first ring plate at the second end of the first set of pusher plates and a second set of the pusher plates are anchored on the second ring plate at the second end of the second set of pusher plates.
Preferably, the clamping device is sound-insulated from at least one of the first ring plate and the second ring plate by means of a soundproofing device. The soundproofing device is advantageously made of a soundproof material, for example rubber. The soundproofing device may further be made in the form of a thin-walled cylindrical membrane.
The electrodes of the piezoelectric element are either applied to flat surfaces of the piezoelectric element or applied to cylindrical surfaces of the piezoelectric element.
The pusher plates are advantageously anchored with a first end in recesses in the piezoelectric element by drafting the recesses.
The rotor is advantageously in the shape of a barrel enclosed by the pusher plates. Alternatively, the rotor is in the shape of a cylinder enclosed by the pusher plates.
Advantageously, either the stator or the rotor switches on the piezoelectric element. Preferably, the transfer of longitudinal oscillations into the first ring plate and the second ring plate from the piezoelectric element takes place via sound-conductive gaskets arranged between the piezoelectric element and the first ring plate and the second ring plate, respectively.
A second embodiment of the invention is a piezoelectric motor comprising a stator and a rotor, the stator and the rotor being in mechanical contact with one another along at least one cylindrical friction surface by means of curved, elastic and longitudinally elongated pusher plates. The pusher plates are held against the friction surface at a first end of the pusher plates, and arranged at an angle to the friction surface. A piezoelectric element is connected to the stator, the piezoelectric element having electrodes placed on opposing surfaces of the piezoelectric element, the piezoelectric element being connectable to an alternating current source via the electrodes for providing longitudinal oscillations in the piezoelectric element. Further, a first ring plate and a second ring plate are arranged on opposite sides of the piezoelectric element, so that at least a portion of surfaces of the piezoelectric element are pressed against surfaces of the first ring plate and the second ring plate, respectively, by a clamping device. In this way, longitudinal oscillations are transferred into the first ring plate and the second ring plate from the piezoelectric element, the pusher plates being anchored on the rotor at a second end of the pusher plates.
Seven alternative methods of attaching the pusher plates to the ring plates are preferred for the second embodiment of the invention:
1) The pusher plates are anchored on the rotor on the first ring plate, for cooperation between the first end of the pusher plates and an inner circumferential surface of the first ring plate.
2) The pusher plates are anchored on the rotor on the second ring plate, for cooperation between the first end of the pusher plates and an inner circumferential surface of the second ring plate.
3) A first set of pusher plates are anchored on the rotor on the first ring plate, for cooperation between the first end of the first set of pusher plates and an inner circumferential surface of the first ring plate, and a second set of pusher plates are anchored on the second ring plate for cooperation between the first end of the second set of pusher plates and an inner circumferential surface of the second ring plate.
4) The diameter of the first ring plate is smaller than a diameter of the second ring plate, and the pusher plates are anchored on the inner circumferential surface of the first ring plate.
5) The diameter of the second ring plate is smaller than a diameter of the first ring plate, and the pusher plates are anchored on the inner circumferential surface of the second ring plate.
6) The diameter of the first ring plate is larger than a diameter of the second ring plate, and the pusher plates are anchored on the inner circumferential surface of the first ring plate.
7) The diameter of the second ring plate is larger than a diameter of the first ring plate, and the pusher plates are anchored on the inner circumferential surface of the second ring plate.
Preferably, the clamping device is sound-insulated from at least one of the first ring plate and the second ring plate by means of a soundproofing device. Advantageously, the soundproofing device is made of a soundproof material, for example rubber. Advantageously, the soundproofing device is made in the form of a thin-walled cylindrical membrane.
The electrodes of the piezoelectric element are applied either to flat surfaces of the piezoelectric element or to cylindrical surfaces of the piezoelectric element.
Preferably, the pusher plates are anchored with a first end in recesses in the piezoelectric element by drafting the recesses.
Advantageously, the rotor is in the shape of a barrel enclosed by the pusher plates. Alternatively, the rotor is in the shape of a cylinder enclosed by the pusher plates.
Preferably, the stator or the rotor switches on the piezoelectric element.
Further features of the invention will be described or will become apparent in the course of the following detailed description.